Process of treating zinc skimmings



o No Drawing.

,nate compounds of chlorine and other impurltlestherefrom. r 5 from galvanizing processes and other proc-J ,"Pat'en ted aw, 1932* 1 I NE Y JE S Y; L nssienoa gbof FEDERATED KENNETH v. B. ROSSMAN, OF- "rimnron,"

METALS CORPORATION, on NEW YORKf 1v, V ,AQVQORPQRATIONY OF. DELAWARE rnocnss or TREATING zinc exit [Mines This invention relates to; a process for treating zinc sklmmings or the like to el1m1- Zinc skimmings comprise a by-product esses wheremetallic zinc, is heated, melted and/or volatilized. Generally the most imi "portantimpurity in zinc skimmings iszinc;

-zincand contribute the impurity ofzinc chlo- 15 r 1 embody'as an average inithe neighborhood of {75% zinc. As much as-5% offthe Zll'lQHlZLY.

f be inthe formof zincchloride, in the neigh-;; V 0

rich .to thezinc skimmings.

chloride arising, from. the use of: certain flux- 7 ing' substances comprising chlorides. I That is, lnithe various-processes of utilizing @zmo, these chloride flux materials combine, withthe Zinc skimmings as commercially available borhood bf 15% may. bepresent as metalliczinc, and the balance is {generally' largely zinc oxide; Small "amounts; of impurities in theform ofchlorldes or oxides of iron, tin,

copper, aluminum and nickel arealso often present, l V 1 In order that the zinc fromsuchskimnnngs 7 may be recovered andfsuccessfully used either iIl'ZlDO smelting or as asource of ZlIlG'Hl'the' manufacture ofzinci by-products, such as; lithopone,;the zinc chloride and other chlorides must be, substantially eliminated,

It is therefore an objectof this invention to'provide a relatively inexpensive-process;

, the zinc.

for substantially eliminating impurities such as chlorides from zinc skimmings and per mittingthe' recovery of a highfpercentage of The invention consists in they process and steps of the process which are herein described according to a preferredmann eraof practicing-the same and the invention will y be more particularly pointed out in the appended claim.

Heretoforein order to enmaae agend 'rine from'zinc skimmings, downrto a very low percentage, the general practicehas been c .to crush and grind the material'in a suitable 7 machine such as a'ball mill, and to screenrthe metallic zinc that 7 Will not pass through an 8 'mesh screen, from the groundskimmings,

. and passes out through settling chambers to a'stack and thence to the air.i:- p

I With such processesicarried out in the orground, and screened sub'stantially: according Application filed January 29,1929. SerialNo. 335022.

The screened arethen heatednin i a rotary kiln and as the material jpasses through the kiln, i the, chlorine is eliminated dinary form ofrotary kilns, the r'ecovery' of $21110 is comparativelylow for various reasons,

importantamong which are the following. A-

considerable portion I of the T nietallic lzinc-gof the -material must necessarily ibecomefso I qulckly raised in 'temperature thatiit' will be r volatilized'and carried outlof thekihnq Also, j ,particlesg'otzmc lwillib'ecarriedout tothe V stack-avith' thef'waste gases; Withfsuch a PrQcess, the rotary kiln presents thefurther r disadvantage that the skimmings remain in constant contactwith thegases of combustion from t-heibu'rnen'. e 1

- Lhaveldiscovered; that the above vantagesi may. beteliminated wi'th rthe consequent recoverywolf higher" percentages of zinc o'ti good quality 'byithe following 'pr-oc ess, which is preferably carried 01min a muh tiple'f' hearth furnace of j the general I type Whichis illustrated, for example, inthe pat-I thoughit will be understoodthat other types ofmultiplehearth furnaces offthe s'ame gen eralcc lass maybe used: A l-furnacedoren-i ample; having nine .hearths including a top dryinggorheatinghearthmaybe' used :The' a zinc s immi'ngs may first be: crushed and tothe customary practice above referred to;

The screened skimmings are thengradually fed into the furnacefand fare slowly'rabbled' Woven-the succeeding 'hearths down through- .thefurnaceew i p 7-: 1 q -In'order thatithe r process fm'ay be carried important to carefully control the tempera lows] The temperature m'aintained atathe top' hearth should he a in} the =:neighborhood 0f-lOOf C. and thetemperatures onlthe suctures within the furnacesubstantiallyjas fol-z ceedingAlower 'hearthsrespectivelyshouldbe ii I increased by substantiallyiuniformifamounts so that thetemperature maintained at the bottom of theefurnace is in the neighborhood of 750 C. By keeping the temperatures within these limits, and thus gradually raising the temperature of the material from hearth to hearth, the metallic zinc thereof 5 becomes largely oxidized, thus precluding volatilization. The zinc losses incurred in the older rocess above referred to are thus substantially eliminated.

The process may be carried out continulo eusly and a limited amount of air is admitted to the furnace; generally sufiicient air will be admitted through the cracks around the furnace doors and at the burner.

With the temperatures above indicated,

the chlorides of the material will be gradually volatilized and will pass out through the upper art of the furnace.

When t e process is carried out in this type of multiple hearth furnace, the flow 23 of gases may be so regulated and limited as to substantially eliminate stack losses of the desired zinc.

7 After a preliminary grinding and screening of the product to be treated whereby as as high as from 15% to of metallic zinc may be removed from the product, the resulting skimmings containing say in the neighborhood of of zinc in the form of oxides and chlorides are treated by the process above as described' According to the processes formerly used the usual maximum recovery of roasted zinc skimmings, that is zinc oxide with minor impurities, amounted to from 79% to 81% of the screened mixture, where- 35 as with the process above described from 85% to 87% of the zinc screenings may be recovered as zinc oxide; the theoretical maximum being in the neighborhood of 90%. The only impurities remaining will be in the form of 0 iron, lead or cadmium oxides and other minor ingredients embodiedin the original skimmmgs which contribute no undesirable charaoteristics to the product.

What I claim as new and desire to secure 46 by Letters Patent is:

Process of substantially eliminating chlorides from zinc skimmings, which comprises introducing same into a multiple hearth furnace, rabbling the zinc skimmings over the several hearths successively while applying, gradually increasing temperatures thereto and with the admission of alimited amount of air, the temperature on the upper hearths bein insuflicient to cause anysubstantial oxi ation of the metallic zinc and the gradually increased temperatures on the succeeding hearths being suflicientto substantially completely eliminate chlorides from the skimmings, and whereb the remaining zinc is oxidized substantial y without vola- In testimony whereof I have signed my name to this specification.

KENNETH V. B. ROSSMAN. 

